I should know the answer to this but on another forum someone's asked this question.

I’ve come across this curiosity a few times in Scotland, but still can’t understand it. The weather front comes from a westerly direction and yet the wind comes from a southerly direction.

I don’t know why this happens, it not always the case but the other day I tracked the front and it was bang on westerly but slow moving, the wind was in excess of 50 knots and from due south.

Anyone know why?

And he adds:

It’s strange that in Derbyshire I’ve never experienced this sort of movement, only in Scotland on the west coast. 

One of the answers he gets is:

Is it not the winds circling the low? The whole weather system is moving west to east but at times the wind could be southerly then, as it passes, you would get the northerlies following the back edge of the system. 

To which he replies. 

I can understand that to a degree, but why doesn’t it do the same when there’s an easterly front?

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An explanation I've heard is that the wind would tend to blow directly from high to low pressure. At ground level, friction between the wind and the ground maintains this situation but higher up Coriolis force is dominant and the wind is diverted to circle the LP.

https://en.wikipedia.org/wiki/Coriolis_force 

An AI search on ' why are upper level winds different from the surface-level winds' returns much the same.

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The direction of wind is not the same as the direction of movement of the weather system.

A front on the southern edge of a low pressure will be moving eastwards as the LP rotates, and the whole system will also likely be moving eastwards on the jet stream. But the wind direction will be more "along the front" so towards the centre of the low. So it is basically the first explanation, as far as I can see.

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Thank you David which ties in with this article I've just come across.

It sets out some contradictions which the author then sets out to correct.

https://weather.mailasail.com/Franks-Weather/Coastal-Wind-Variatios 

The reason is that a cooler surface creates what is known as an "internal boundary layer" in which cool, dense air stays near the surface and tends to back to run more towards low pressure - ie across the isobars. To understand this, remember that at the top of the boundary layer, the Coriolis effect will cause air to move nearly along the isobars - the Gradient Wind. The slower moving air near the surface is less deflected by Coriolis and, so, moves more towards low pressure. This can be seen on a clear night with light winds. Surface winds may blow nearly at right angles to the isobars.

It ties in with my own observations on a local coastline I'm familiar with. The Met Office are uncannily locally correct with the wind direction and speeds but tend to fail on the precipitation. When for example the wind is from an easterly direction, the general South West England forecast will go for calm overnight but the very local Ringstead one will forecast F2 to 3 even 4 ENE winds for a very local stretch of coast. Their model obviously uses its local knowledge/past data to do this.  Or at least that's how I see it. 

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You can sometimes tell how active a front is as well by the isobar alignment before the front itself. A warm front with a tight isobar gradient running parallel and ahead of it can mean that lot of rain is on the way. More likely to be seen if the warm front is moving up from the south or southwest and pushing up against a particularly cold airmass. 

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